Collision avoidance system having GPS enhanced with OFDM transceivers

ABSTRACT

An object relative status determination system ( 54 ) for a vehicle ( 52 ) includes an orthogonal frequency domain modulation (OFDM) transceiver ( 56 ) that generates an object range signal ( 83 ). The system ( 54 ) may also include a global navigation system (GNS) ( 58 ) that receives a satellite range signal ( 70 ). A controller ( 66 ) is coupled to the OFDM transceiver ( 56 ) and the GNS ( 58 ) and determines object information relative to the vehicle ( 52 ) in response to the object range signal ( 83 ) and the satellite range signal ( 70 ).

TECHNICAL FIELD

The present invention relates to collision warning, avoidance, andcountermeasure systems for an automotive vehicle. More particularly, thepresent invention is related to systems and methods of determiningpositions and velocities of vehicles relative each other.

BACKGROUND OF THE INVENTION

Collision warning, avoidance, and countermeasure systems are becomingmore widely used. Collision warning systems are able to detect an objectwithin proximity of a host vehicle and assess whether the objectdetected is an obstacle and poses a threat to the host vehicle. Thesesystems also provide a vehicle operator knowledge and awareness ofobstacles or vehicles within a close proximity in time such that theoperator may perform actions to prevent colliding with the detectedobstacles. Countermeasure systems exist in various passive and activeforms. Some countermeasure systems are used in the prevention of acollision others are used in the prevention of an injury to a vehicleoperator.

Collision warning systems maybe forward or rearward sensing. Thesesystems can indicate to a vehicle operator that an object, that may notbe visible to the vehicle operator, is within a stated distance andlocation relative to the host vehicle. The vehicle operator may thanrespond accordingly. Other collision warning systems and countermeasuresystems activate passive countermeasures such as air bags, load limitingseat belts, or active vehicle control including steering control,accelerator control, or brake control whereby the system itself aids inpreventing a collision or injury.

Many countermeasure systems require knowledge of locations andvelocities of objects or vehicles that are proximate to a host vehicle.Global Navigation Systems (GNS), such as the United States GlobalPositioning System (GPS) and other similar systems that are based onsimilar principles, such as the Russian Federation Glasnost system, thePeople's Republic of China Beidou (Big Dipper) system, and the EuropeanUnion Galileo system can provide this information, but frequentlywithout the necessary accuracy.

A typical GPS vehicle scenario includes multiple vehicles equipped withGPS receivers that are coupled to onboard computers equipped withtwo-way digital radios for communications therebetween. Position,velocity, and time (PVT) data is computed in the GPS receivers andpassed to the computers. The PVT data may be exchanged between thevehicles using the two-way radios, or through use of wireless modems ornetwork devices. Several protocols are established for performing thisexchange of PVT data, which includes Dedicated Short RangeCommunications (DSRC) and Institute of Electric and ElectronicsEngineers (IEEE) 802.11a specification protocols. A typical or normalGPS calculates PVT data using the time of travel of signals from asystem of satellites to a GPS receiver. In this process many of the usererrors attributable to GPS measurements are eliminated. However, theerrors attributed to the GPS receivers cannot be eliminated by such asubtraction and the errors, as a result, are multiplied or amplified indetermining position. The size of these errors is sensitive to thegeometric relationship between GPS satellites being used.

Additionally, in using current GPS, each vehicle's GPS must be able toreceive signals from at least four satellites simultaneously for theproper functioning thereof. Buildings, overpasses, foliage, and terrainmay limit the number of satellites that are “visible” to the receiversof a GPS. Thus, these limitations reduce the effectiveness of currentGPSs in determining vehicle PVT data for the purposes of vehicle safety,navigation, and Telematics.

Thus, there exists a need for an improved system for determiningrelative positioning and velocity data for an automotive vehicle thatminimizes the above-stated errors and is not limited by the number ofvisible GPS satellites.

SUMMARY OF THE INVENTION

The present invention provides an object relative status determinationsystem for a vehicle. The system includes an orthogonal frequency domainmodulation (OFDM) transceiver that generates an object range signal. Thesystem may also include a global navigation system (GNS) that receives asatellite range signal. A controller is coupled to the OFDM transceiverand the GNS and determines object information relative to the vehicle inresponse to the object range signal and the satellite range signal.

The embodiments of the present invention provide several advantages. Onesuch advantage is the provision of communicating vehicle informationwith respect to a host vehicle utilizing orthogonal frequency domainmodulation transceivers. In so doing, the stated embodiment aids in thereducing of the number of satellites that need to be visible whileincreasing the accuracy of the measurements performed.

Another advantage provided by an embodiment of the present invention, isthe provision of an OFDM based object information system that isself-contained and packaged to be easily installed or retrofit intovarious vehicles.

Yet another advantage provided by an embodiment of the presentinvention, is the provision of a an OFDM based object information systemthat is in communication with other onboard vehicle systems, such as anavigation system, a telematics system, and a collision warning,avoidance, and countermeasure system.

The present invention itself, together with attendant advantages, willbe best understood by reference to the following detailed description,taken in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention reference should nowbe had to the embodiments illustrated in greater detail in theaccompanying figures and described below by way of examples of theinvention wherein:

FIG. 1 is a block diagrammatic view of object relative informationsystems utilizing GPSs and two-way radios and applied to a vehiclesituation;

FIG. 2 is a top view of a sample vehicle intersection situation for apair of vehicles each having a GPS and a two-way radio;

FIG. 3 is a top view of a sample vehicle merging situation for a pair ofvehicles each having a GPS and a two-way radio;

FIG. 4 is a sample position diagram for a GPS of a vehicle;

FIG. 5 is a block diagrammatic view of an OFDM based object informationsystem in accordance with an embodiment of the present invention;

FIG. 6 is a logic flow diagram illustrating a method of determiningobject information relative to a vehicle in accordance with multipleembodiments of the present invention;

FIG. 7 is a sample position diagram for a pair of vehicles utilizingobject relative status determination systems in accordance with anembodiment of the present invention;

FIG. 8 is a sample position diagram for a series of vehicles utilizing aplatooning method in accordance with an embodiment of the presentinvention;

FIG. 9 is a sample position diagram for a series of vehicles utilizinganother platooning method in accordance with another embodiment of thepresent invention; and

FIG. 10 is a sample logic flow diagram and block schematic illustratingan OFDM communication modulation scheme in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

GPS errors are normally categorized as either system errors or usererrors. System errors are errors that arise from a GPS system itself.The system errors, for example, can include synchronization errorsbetween satellites, synchronization errors with a central clock,inaccuracies in satellite PVT data, number of visible satellites at anygiven time, velocity and timing aspects within the satellites, andaccuracy of the timing signal shape. Also, the relative position of thesatellites affects geometric dilution of precision (GDOP), whichamplifies range errors. Range errors refer to the distance between thesatellites and the GPS receivers. Small angle between the range linescauses high GDOP. High GDOP refers to magnification in measurementserrors in the length of the range lines due to the satellites beinglocated near the horizon.

User errors are errors that can be minimized within the GPS receivers.User errors include receiver errors and environmental errors. Receivererrors are a result of circuit limitations of the receivers, such asthermal amplifier noise, receiver clock error, as well as errors due tosignal processor sampling rates and simplifications of PVT calculationsto accommodate available CPU power. Receiver errors can be minimized bythe increased ability of a receiver to calculate PVT data in response toan increased number of satellite ranges or ranges from an increasednumber of satellites. At least four satellite ranges are needed tocompute the four PVT unknowns, which are longitude, latitude, elevation,and time.

Some receiver errors can be reduced by averaging data from severalreceivers. However, a more effective method of reducing error is derivedfrom reducing environmental errors when the relative position andvelocity of two vehicles is desired. Environmental errors are caused byenvironmental factors that affect the signals transmitted by satellites.Environmental factors include multipath fading, reflected signals,blocked signals, spatial variance in atmospheric impedance, thermalnoise added in the atmosphere, and jamming sources, such as Ultra-WideBand (UWB) transmitters.

Many of the environmental factors are the same for two closely spacedvehicles. When relative PVT information is determined for the closelyspaced vehicles through subtraction thereof, many of the environmentalerrors are cancelled.

The present invention not only minimizes receiver and environmental, butalso system errors as is described in further detail below. Also, thepresent invention provides improved geometry of the range measurements,especially when satellites are not located near the horizon relative toa vehicle. Horizontal range information is derived from thetime-of-flight of OFDM signals. Since the OFDM signals travel a shortdistance between vehicles, environmental factors are negligible. Also,the path that the OFDM signals travel is close to or approximately thesame in length as the path that is measured, thus reducing the GDOP.

In the following figures the same reference numerals will be used torefer to the same components. While the present invention is describedwith respect to systems and methods of determining positions andvelocities of vehicles relative to a host vehicle, the present inventionmay be adapted and applied to various systems including: collisionwarning systems, collision avoidance, systems, parking aid systems,reversing aid systems, countermeasure systems, vehicle systems,navigation systems, telematic systems, Cooperative Adaptive CruseControl systems or other systems that may require object position orvelocity determination. The present invention may be applied invehicles, such as cars, trucks, buses, and boats. The present inventionmay also be utilized in a portable format for use by bicyclists andpedestrians. The present invention may be applied to any applicationwhere proximity measurements are performed.

The present invention may also be utilized in stationary locations, suchas at an intersection, a dock, a shopping mall, an urban canyon, orother stationary locations to supplement a standard GNS. The positioningalgorithm of embodiments of the present invention is capable ofoperating with less than four visible satellites, which allows for usein low satellite visibility areas where GNS signals are blocked, some ofwhich are mentioned above. Stationary OFDM based systems and pseudolitesmay be utilized as described below in providing this capability.

In the following description, various operating parameters andcomponents are described for one constructed embodiment. These specificparameters and components are included as examples and are not meant tobe limiting.

Also, in the following description the term “performing” may includeactivating, deploying, initiating, powering, and other terms known inthe art that may describe the manner in which a passive countermeasuremay be operated.

Additionally, in the following description the term “countermeasure” mayrefer to reversible or irreversible countermeasures. Reversiblecountermeasures refer to countermeasures that may be reset to theiroriginal form or used repeatedly without a significant amount offunctional deficiency, which may be determined by a system designer.Irreversible countermeasures refer to countermeasures such as airbagsthat, once deployed, are not reusable.

Moreover, a countermeasure signal may include information pertaining tothe above-stated reversible and irreversible countermeasures or mayinclude other information, such as collision warning information. Forexample, the countermeasure signal may contain object detectioninformation, which may be used to indicate to a vehicle operator thepresence or close proximity of a detected object.

Referring now to FIG. 1, a block diagrammatic view of object relativeinformation systems 10 utilizing GPSs 12 and two-way radios 14 asapplied to a vehicle situation is shown. Each of the GNSs or GPSs 12includes a controller 16. The controllers 16 determine the approximateposition of vehicles A and B in a Cartesian coordinate system (notshown). GPSs, in general, indicate PVT data using the 1984 WorldGeodetic System (WGS84) or Universal Transverse Mercator (UTM)coordinates, which are readily converted to a flat Cartesian coordinatesystem. WGS84, UTM, and similar geodetic system describe the coordinatesystem of the position and time values. Position, velocity, and time(PVT) data 18 is collected in the GPSs 12 and received by thecontrollers 16. This data may be collected from the GPSs 12 usingNational Marine Electronics Association (NMEA) communications standards.NMEA is used to determine the type of physical wire used, the type ofsignals that travel over the wire, the type of data encoding, and thetype of data packet format. The PVT data 18 is exchanged between thevehicles A and B using the two-way radios 14. Although the two-wayradios 14 are shown, the PVT data 18 may be exchanged utilizing wirelessmodems or network devices, such as those that conform to the IEEE802.11a or Dedicated Short Range Communications (DSRC) specifications.

Known position and velocity vectors of the vehicles A and B aresubtracted to provide relative velocity vectors. The controllers 16 candetermine whether the vehicles A and B are traveling such that they maypotentially collide in response to the relative positions and velocitiesof the vehicles A and B. The controllers 16 may perform a countermeasurewhen there exists a high probability of vehicles A and B colliding.

Referring now to FIG. 2, a top view of a sample vehicle intersectionsituation for a pair of vehicles A′ and B′ each having a GNS or GPS 20and a two-way radio 22 are shown. The vehicles A′ and B′ have objectrelative information systems 24, such as those described above withrespect to FIG. 1. The first vehicle A′ is traveling in an eastwarddirection along roadway x. The second vehicle B′ is traveling in anorthbound direction along roadway y. Positions of the vehicles A′ andB′ may be determined utilizing equations 1-6, with reference to roadwaysx and y, where R is the-altitude of vehicle A′ relative to the center ofthe earth, D is the distance between the vehicles A′ and B′, and BR isthe bearing from vehicle A′ to vehicle B′. Although equations 1-4 and 6are shown with respect to vehicle A′, the equations may be easilymodified to be in respect to vehicle B′. $\begin{matrix}{\theta = {\frac{2\pi}{360}\left( {{{Latitude}\quad{of}\quad{vehicle}\quad A^{\prime}} - {{Latitude}\quad{of}\quad{vehicle}\quad B^{\prime}}} \right)}} & (1) \\{\phi = {\frac{2\pi}{360}\left( {{{Longitude}\quad{of}\quad{vehicle}\quad A^{\prime}} - {{Longitude}\quad{of}\quad{vehicle}\quad B^{\prime}}} \right)}} & (2) \\{y = {2R\quad{\sin\left( \frac{\theta}{2} \right)}}} & (3) \\{x = {\left\lbrack {\pi\quad R\quad{\cos\left( {{Latitude}\quad{of}\quad A^{\prime}} \right)}} \right\rbrack{\sin(\phi)}}} & (4) \\{D = \sqrt{x^{2} + y^{2}}} & (5) \\{{BR} = {\arctan\left( \frac{x}{y} \right)}} & (6)\end{matrix}$

Velocities of the vehicles A′ and B′ may be determined utilizingequations 7-8, where x is the relative velocity vector for vehicle A′and {dot over (y)} is the relative velocity vector for vehicle B′. Thebearings of vehicles A′ and B′ with respect to North as determined bythe GPSs 20 are θ_(A) and θ_(B), respectively. The speeds of vehicles A′and B′ as determined by the GPSs 20 are S_(A) and S_(B), respectively.The relative velocity vector between the vehicles A′ and B′ is$\left\{ {\overset{.}{x},\overset{.}{y}} \right\}.${dot over (x)}=S _(A′) sin(θ_(A′))+S _(B′) sin(θ_(B′))   (7){dot over (y)}=S _(A′) cos(θ_(A′))+S _(B′) cos(θ_(B′))   (8)

When the relative velocity vector$\left\{ {\overset{.}{x},\overset{.}{y}} \right\}$is parallel with a bearing vector of one of the vehicles A′ or B′′then acollision may occur unless corrective actions are performed. Themagnitude of the distance D divided by the magnitude of the velocityvector $\left\{ {\overset{.}{x},\overset{.}{y}} \right\}$is approximately equal to the time to collision T_(c) of the vehicles A′and B′, which is represented by equation 9. $\begin{matrix}{T_{c} = {\frac{\left\{ {x,y} \right\}}{\left\{ {\overset{.}{x},\overset{.}{y}} \right\}}}} & (9)\end{matrix}$

A collision factor C may be determined using equation 10. When C isequal to zero, vehicles A′ and B′ are traveling such that they maycollide with each other. $\begin{matrix}{C = {{\left\{ {x,y} \right\} \times \left\{ {\overset{.}{x},\overset{.}{y}} \right\}} = {{x\quad\overset{.}{y}} - {\overset{.}{x}\quad y}}}} & (10)\end{matrix}$Although equations 1-10 are utilized above with respect to singlevehicle situation, the equations may be applied to various other vehiclesituations. For example, the equations may be applied to avehicle-merging situation, as shown in FIG. 3. FIG. 3 is a top view of asample vehicle merging situation for a pair of vehicles A″ and B″ eachhaving a GPS 26 and a two-way radio 28, similar to that of vehicles A,A′, B, and B′ above.

Referring now to FIG. 4, a sample position diagram for a GNS or GPS 30of an automotive vehicle 32 is shown. The GPS 30 determines position ofthe vehicle 32 in response to satellite range signals 34 received fromthe satellites 36. The satellites 34 may include one or morepseudolites, such as pseudolite 38. Pseudolites represent simulatedsatellites and may for example be in the form of a beacon. Pseudolitesare utilized when some or all of the satellites 36 are not visible tothe GPS 30. This may occur when the vehicle 32 is in a parking garage,under an overpass, or when portions of a building or foliage areobstructing communications between the satellites 36 and the GPS 30.

Position of the vehicle 32 may be determined using equations 11-13,where P_(J) is the distance between satellite J and the GPS 30, where Jis one of the satellites 36, c is the speed of light, ΔT is the amountof time for a signal to travel from satellite J and reach the GPS 30, tis the time difference between a GPS clock 40 and a satellite clock 42,and N is the number of satellites 36.P_(j)=cΔT   (11)P _(j)={square root}{square root over ((x _(j) −x _(u))²)}+(y _(j) −y_(u))²+(z _(j) −z _(u))² +ct; for j−1 . . . N   (2)P _(j) =f(x _(u) , y _(u) , z _(u) , Δt)   (13)

The position of each satellite 36 is x_(J),y_(J),z_(J). The position ofthe GPS 30 is x_(u),y_(u),z_(u). Non-linear equation 13 may be solvedusing linearization of f(x_(u),y_(u),z_(u),Δt) and iteration, closedform solutions, or Kalman filtering as is known in the art.

Referring now to FIG. 5, a block diagrammatic view of an OFDM basedobject information system 50 in accordance with an embodiment of thepresent invention is shown. The OFDM based system 50 includes multiplevehicles. 52, each of which having an object relative statusdetermination system 54 and 54′, respectively, each having one or moreOFDM transceivers 56. The object systems 54 and 54′ have a GNS or GPS 58that includes a GPS antenna 60, a radio frequency unit 62, a digitalsignal processor 64, and a main controller 66. The GPSs 58 are incommunication with one or more satellites 68, which are best seen inFIG. 7. The satellites 68 may be replaced with one or more pseudolites,NAVSAT satellites, or the like. GPS signals or satellite range signals70 are received by the GPS antenna 60 and the radio frequency units 62,are filtered and conditioned via the processors 64, and are utilized bythe controllers 66 to determine position of an associated vehicle.

The OFDM transceivers 56 are utilized to determine relative range andvelocity of the vehicles with respect to each other, and also tocommunicate range, velocity, and PVT information used in the positioningcalculation. Time-of-flight and Doppler shifts between OFDM transceiversare used in determining PVT information. For example, the OFDMtransceivers 72 of a first or host vehicle 74 may communicate with theOFDM transceivers 76 of a second vehicle 78 and a third vehicle 80 todetermine relative position and velocity of the second and thirdvehicles 78 and 80 relative to the host vehicle 74.

The OFDM transceivers, 56 are in communication via an OFDM Media AccessProtocol (MAC) vehicle network interface 82. The OFDM interface 82allows many mobile devices to interoperate in the same radio frequencyband. The OFDM interface 82 utilizes an ad hoc mode whereby there is nohierarchy between mobile nodes. This is unlike that of a Bluetooth typeMAC, which operates under the constraint of frequency hopping narrowband modulation and requires the use of Piconets and Scatternets inwhich nodes have master, slave and master/slave functions. The OFDMtransceivers 56 transmit and receive object range signals 83, as well asother signals between each other via the vehicle network 82.

Each vehicle 52 may have any number of OFDM transceivers. In oneembodiment of the present invention, a first OFDM transceiver 72 _(A) isutilized for discovery services and a second OFDM transceiver 72 _(B) isutilized for range and synchronization services. Discovery services mayinclude the detection of vehicles, whereas the range and synchronizationservices may include the determination of relative range, range rate,and the synchronization of communication with detected vehicles.

The OFDM transceivers 56 are equipped for range finding,synchronization, and Doppler velocity measurements. The OFDMtransceivers 56 are utilized in conjunction with the GPSs 58 tosynchronize clocks 84 on each vehicle 52 with the clocks 86 on thesatellites 68. Although the OFDM transceivers 56 and the GPSs 58 areshown as separate components they may be integrally formed into a singleunit, such as a solid-state logic device, integrated logic chip, or asystem-on-chip (SOC). The OFDM transceivers 56 and the GPSs 58 may bebattery powered, powered by a vehicle power source, or may be externallypowered.

Time synchronization can be achieved for a group of GPSs, when each GPSis coupled to a pair of OFDM transceivers, such as the. GPS 58A andtransceivers 72. Each OFDM transceiver 72 has a direct connection tomultiple neighbor or other OFDM transceivers in proximity therewith,such as OFDM transceivers 56. This creates a string or mesh topologynetwork on which the synchronization is performed.

Synchronized time is computed as part of the PVT calculation. Fourunknowns are calculated, the position in three spatial dimensions andthe time of arrival of simultaneously transmitted timing signals fromfour objects having known positions. The timing signals may be GPSsignals from satellites or OFDM signals from other vehicles orstationary OFDM based systems. The positions of the four objects areknown and are transmitted as part of the timing signals. The PVTcalculation may be improved through use of higher order time derivativesof position, such as that derived from acceleration and jerk. Whenposition of less than four objects are known a PVT calculation may beperformed, assuming a particular spatial value, such as the altitude ortime, which may be extrapolated using an accurate clock.

Since the OFDM transceivers 56 are coupled to the GPSs 58, they can beutilized to support differential GPS, interferometric methods, such ascarrier-phase differential GPS, and other GPS techniques known in theart. Also, since the GPSs 58 are wirelessly coupled via the OFDMtransceivers 56, they may share ephemeris information, which candecrease time involved in the cold start process of the GPSs 58. Forinstance, when a GPS unit does not have current location information ofNAVSAT satellites, download time to acquire such information may beapproximately 12.5 to 25 minutes in length. The GPS on a first vehiclemay receive the ephemeris data, via a first OFDM transceiver, from asecond vehicle having a second OFDM transceiver in fractions of amillisecond.

The object systems 54 may also include various vehicle dynamic sensors90, active countermeasures 92, passive countermeasures 94, an indicator96, a navigation system 98, and a telematics computer 100, which may allelectrically coupled to the controllers 66. The main controllers 66 mayactivate the countermeasures 92 and 94 or indicate to a vehicle operatorvarious object and vehicle information, via the indicator 96, to preventa vehicle collision and injury to vehicle occupants.

The main controllers 66 may be microprocessor based such as a computerhaving a central processing unit, memory (RAM and/or ROM), andassociated input and output buses. The main controllers 66 may be aportion of a central vehicle main control unit, an interactive vehicledynamics module, a restraints control module, a main safety controller,or may be a stand-alone controller as shown. The main controllers 66 maycommunicate therebetween via the OFDM transceivers 56, the vehiclenetwork 82, the MAC interface, or a combination thereof, as is shown bysignals 83 and 89.

The vehicle dynamics sensors 90 may include a transmission rotationsensor, a wheel speed sensor, an accelerometer, an optical sensor, orother velocity or acceleration sensors known in the art. The vehicledynamic sensors 90 can be used to measure the dynamic state of thevehicle 74. This can be transmitted to other vehicles using the OFDMdevices 56 and used to aid the PVT calculation.

Active countermeasures 92 may refer to the control of a brake system, adrivetrain system, a steering system, a chassis system control, or mayrefer to other active countermeasures known in the art.

The passive countermeasures 94 may refer to air bags, pretensioners,inflatable seat belts, a load limiting pedal and steering column, or mayrefer to other passive countermeasures and control thereof. Some otherpossible passive countermeasures that may be included are seatbeltcontrol, knee bolster control, head restraint control, load limitingpedal control, load limiting steering control, pretensioner control,external airbag control, and pedestrian protection control. Pretensionercontrol may include control over pyrotechnic and motorized seatbeltpretensioners. Airbag control may include control over front, side,curtain, hood, dash, or other type airbags. Pedestrian protectioncontrol may include controlling a deployable vehicle hood, a bumpersystem, or other pedestrian protective devices.

The indicator 96 is used to signal or indicate a collision-warningsignal or an object identification signal in response to relative rangeor velocity information of nearby objects or vehicles. The indicator 96may include a video system, an audio system, an LED, a light, globalpositioning system, a heads-up display, a headlight, a taillight, adisplay system, a telematic system or other indicator. The indicator 96may supply warning signals, collision-related information,external-warning signals to objects or pedestrians located outside ofthe vehicle, or other pre and post collision information.

Referring now to FIGS. 6 and 7, a logic flow diagram illustrating amethod of determining object information relative to a host vehicle U asample position diagram for a pair of vehicles, including vehicle U anda vehicle W, are shown in accordance with multiple embodiments of thepresent invention. The vehicles U and W utilize object systems 54″ thatare similar to object systems 54.

In step 200, positions of the vehicles U and W are determined utilizingthe GPSs 58′. In step 200A, the GPSs 58′ receive satellite range signals70 from the satellites 68 and in response thereto determine range ofeach satellite 68 of interest relative to each vehicle U and W. Thesatellite ranges P_(JU) and P_(JW) with respect to vehicles U and W, aredetermined utilizing equations 14-15, where as stated above J is one ofthe satellites 68, c is the speed of light and t is the time differencebetween the GPSs 58′ or clocks therein. P_(JU) is the distance betweenthe satellite J and the vehicle U. P_(JW) is the distance between thesatellite J and the vehicle W.P _(JU)={square root}{square root over ((x _(J) −x _(U))²+(y _(J) −y_(U))²+(z _(J) −x _(U))²)}+ct=f(x _(U) ,y _(U) ,z _(u) ,Δt); for J=1 . .. N (14)P _(JW){square root}{square root over ((x _(J) −x _(W))²+(y _(J) −y_(W))²+(z _(J) −z _(W))²)}ct=f(x _(X) ,y _(W) ,z _(W) ,Δt); for J=1 . .. N   (15)

In step 200B, the positions of the vehicles (x_(U),y_(U),z_(U)) and(x_(W),y_(W),z_(W)) are determined in response to the ranges P_(JU) andP_(JW) using techniques known in the art.

In step 202, instead of the GPSs 58′ determining positions, velocity,and time (PVT) information and transmitting the PVT information betweenthe vehicles U and W as with the systems 10 of FIG. 1, the OFDMtransceivers 56′ are utilized to determine range of the vehicles U and Wrelative to each other. The OFDM transceivers 56′ generate, transmit,and receive, vehicle-to-vehicle OFDM range signals or object rangesignals 120. Distance D between the vehicles U and W is determined usingequation 16. Distance D is determined using OFDM time of flightmeasurements.D={square root}{square root over ((x _(U) −x _(W))²+(y _(U) −y _(W))²+(z_(U) −z _(W))²)}  (16)

In step 204, relative velocity of the vehicles U and W is determined bymeasuring the Doppler shift in the object range signals and usingequations 17-19. As such, the rate of change in the ranges P_(JU) andP_(JW) and distance D are determined. {dot over (P)}_(JU) is the timerate of change in the distance between the satellite J and the vehicleU. {dot over (P)}_(JW) is the time rate of change in the distancebetween the satellite j and the vehicle W. {dot over (D)} is the timerate of change in the distance between the vehicles U and W. The rate ofchange in distance {dot over (D)} is determined by measuring the Dopplershift in the OFDM signal. $\begin{matrix}{{{{\overset{.}{P}}_{JU} = {\sqrt{\left( {{\overset{.}{x}}_{J} - {\overset{.}{x}}_{U}} \right)^{2} + \left( {{\overset{.}{y}}_{J} - {\overset{.}{y}}_{U}} \right)^{2} + \left( {{\overset{.}{z}}_{J} - {\overset{.}{z}}_{U}} \right)^{2}} + {c\overset{.}{t}}}};}{{{for}\quad J} = {1\quad\ldots\quad N}}} & (17) \\{{{{\overset{.}{P}}_{JW} = {\sqrt{\left( {{\overset{.}{x}}_{J} - {\overset{.}{x}}_{W}} \right)^{2} + \left( {{\overset{.}{y}}_{J} - {\overset{.}{y}}_{W}} \right)^{2} + \left( {{\overset{.}{z}}_{J} - {\overset{.}{z}}_{W}} \right)^{2}} + {c\quad\overset{.}{t}}}};}{{{for}\quad J} = {1\quad\ldots\quad N}}} & (18) \\{\overset{.}{D} = \sqrt{\left( {{\overset{.}{x}}_{J} - {\overset{.}{x}}_{W}} \right)^{2} + \left( {{\overset{.}{y}}_{U} - {\overset{.}{y}}_{W}} \right)^{2} + \left( {{\overset{.}{z}}_{U} - {\overset{.}{z}}_{W}} \right)^{2}}} & (19)\end{matrix}$

The velocities of the satellite J and the vehicles U and W are$\left( {{\overset{.}{x}}_{U},{\overset{.}{y}}_{U},{\overset{.}{z}}_{U}} \right),\left( {{\overset{.}{x}}_{U},{\overset{.}{y}}_{U},{\overset{.}{z}}_{U}} \right),$and$\left( {{\overset{.}{x}}_{W},{\overset{.}{y}}_{W},{\overset{.}{z}}_{W}} \right),$respectively.

In step 206, the OFDM transceivers 56′ also synchronize the clocks 84′of each of the GPSs 58′. The use of the OFDM transceivers 56′ reducesthe number of satellites that need to be visible. Since in general fourranges are needed to compute the PVT data, and since the OFDM basedsystem 50 is capable of using OFDM ranging information from a nearbyvehicle or from a stationary OFDM based system instead of from asatellite, the number of visible satellites required is reduced.

Steps 202-206 may be performed simultaneously. Other forms of equations14-19 may be used. The ranges and velocities may also be determinedusing aid or information from other devices contained within thevehicles U and W that use the OFDM transceivers 56′ and GPSs 58′. Forexample, navigation data, vehicle speed data, and accelerometer data maybe used to improve the accuracy of the range and velocity calculationsor to reduce the number of satellites visibly needed to perform thestated calculations.

In step 208, the main controllers of the systems 54″, such as thecontrollers 66 of the systems 54, may generate countermeasure signals inresponse to the calculated relative ranges and velocities. In step 210,the main controllers may perform one or more countermeasure or warn avehicle operator via an indicator, such as indicator 96 of FIG. 5, inresponse to the countermeasure signals.

The above-described steps are meant to be an illustrative example; thesteps may be performed sequentially, synchronously, simultaneously, orin a different order depending upon the application.

Although the above method and the system are described in respect to anapproaching or following type scenario, the above method and system maybe utilized in various vehicle and object scenarios, such as mergingscenarios, lane change scenarios, intersection scenarios, approachinghead-on scenarios, following scenarios, and other scenarios known in theart.

Referring now to FIG. 8, a sample position diagram for a series ofvehicles 130 utilizing a platooning method in accordance with anembodiment of the present invention is shown. The OFDM based system 50may be utilized when joining a group of vehicles in a formation, such asa platoon. The term “platooning” refers to when vehicles move near oneanother such that there is little space between the vehicles and mayalso refer to the techniques utilized to determine relative positioning,range, and velocities of the vehicles therein. Platooning is used toreduce total wind drag or improve aerodynamics on a group of vehiclesfor improved fuel economy. Platooning also creates open spaces intraffic for vehicles to reside or pass therethrough, which aids intraffic congestion control.

To successfully platoon the vehicles 130, control algorithms areimplemented to control the positioning and velocity of each of thevehicles 130. The vehicles 130 have OFDM links 132 therebetween.

In the platooning scheme as shown, the vehicles 130 include a headvehicle 134, multiple middle vehicles 136, and a tail vehicle 138. Inthe shown embodiment, instead of each vehicle 130 requiring foursatellite-GPS links, one or more satellite-GPS links 142 are used permiddle vehicle 136, two satellite-GPS links 142 are used for each of thehead and tail vehicles 134 and 138. Vehicle 143 can be located from timeand elevation data in addition to the ranging signals received from themiddle vehicle 144 and the tail vehicle 138. Thus, vehicle 143 does notneed to receive ranging signals from any of the satellites 68′. Vehicles130 may receive timing and elevation data from neighboring vehicles orfrom the satellite-GPS links 142.

Also for the platooning scheme shown in FIG. 8, there are 6N+1 degreesof freedom or range, velocity, and time measurements for an N number ofvehicles. Range and rate of change in range are measured by the OFDMtransceivers 56″ and by the GPSs 58″. There are 3N range and velocitymeasurements and one time measurement performed. The OFDM transceivers56″ are used to synchronize the GPSs 58″. The middle vehicles 136 needonly have visible one satellite or pseudolite, since they have OFDMlinks 132 to a vehicle forward and rearward thereof, unless otherinformation is provided as stated below. The head vehicle 134 and thetail vehicle 138 need a minimum of two satellites or pseudolites to bevisible, unless other information is provided as stated below.

Referring now to FIG. 9, another sample position diagram for a series ofvehicles 130′ utilizing another platooning method in accordance withanother embodiment of the present invention is shown. Two satellite-GPSlinks 142 are used per middle vehicle 136′, three satellite-GPS links142 are used for the head vehicle 134′ and the rear vehicle 138′.Vehicles 130′ may receive timing and elevation data from neighboringvehicles via the OFDM links 132 or from the satellite-GPS links 142.

Other information and assumptions can be used in a platoon of vehiclesto further reduce the number of satellite-GPS links and improve accuracyof the calculations, such as navigation data and velocity andacceleration data. For example, since it is generally known that avehicle travels on the surface of the earth, vertical possible travelingplanes or paths can be assumed or minimized and thus, satellitedependency can be reduced.

Referring now to FIG. 10, a logic flow diagram and block schematicillustrating an OFDM communication modulation scheme in accordance withan embodiment of the present invention is shown.

In step 300, a first 2N vector of bits in a first known pattern areencoded into a first 2N/M vector of amplitude and phase symbols, where Nis a pre-determined value and M is the number of elements in a symbolset. In step 302, an inverse Fast Fourier Transform is performed on thefirst vector of amplitude and phase symbols to form a first 2N/M vectorof amplitudes. In step 304, the first vector of amplitudes is convertedfrom a digital format to an analog format over a packet time interval.

In step 306, the analog formatted first vector of amplitudes isamplified and transmitted, via an OFDM transceiver, such as one of thetransceivers 56. In step 308, a second analog formatted 2N/M vector ofamplitudes is received and amplified. The second vector of amplitudes isthe same as the first vector of amplitudes except that it has a timedelay.

In step 310, the second vector of amplitudes is converted into a digitalformat over a packet time interval. In step 312, a reference 2N vectorof bits having a second known pattern, similar to the first knownpattern, is encoded into a second 2N/M vector of amplitude and phasesymbols. The second vector of amplitude and phase symbols is similar tothe first vector of amplitude and phase symbols. In step 314, the secondvector of amplitudes and phase symbols are Fast Fourier Transformed intoa third 2N/M vector of amplitudes.

In step 316, the digitally formatted second 2N/M vector of amplitudes iscompared with the third 2N/M vector of amplitudes to determinetime-of-flight. Time-of-flight information is determined for thetransmitted signal or the transmitted first vector of amplitudes. As anexample, amplitude peaks of the second and third vectors of amplitudesare compared, which may be referred to as OFDM packets, to determine thetime delay between transmission and reception. The initial peakdifference in amplitude between the second and third vectors ofamplitudes provides an accurate time correlation. Of course, othermethods may be utilized to determine time-of-flight.

In step 318, the second vector of amplitudes is Fast Fourier Transformedto form a third 2N/M vector of amplitudes and phase symbols. In step320, the second vector of amplitudes and phase symbols is compared withthe third vector of amplitudes and phase symbols in the frequency domainto determine the Doppler shift therebetween. The initial peak differencein power between the second and third vectors of amplitudes and phasesymbols provides an accurate Doppler shift correlation.

The present invention provides an object relative status determinationsystem that utilizes information from both a GPS and an OFDMtransceiver. This combination reduces the dependency on visiblesatellites and improves accuracy of relative range and velocitymeasurements. The range, velocity, and synchronization provided withOFDM protocol reduce the number of required visible satellites andpseudolites while increasing the accuracy of PVT measurements. Thestatus determination system is capable of accurately performingproximity measurements when signal paths are obscured. The statusdetermination system also improves GPS data for vehicle navigation andother-purposes, as well as vehicle safety and pre-collision sensing.Since GPS and OFDM receivers detect system failures, fail over methodsare easy to implement.

The relative status determination system in using OFDM providesdecreased susceptibility to Doppler shift caused by the relative motionof mobile devices and to multipath fading. The highly packetized natureof OFDM provides accurate time-of-flight measurements. Since OFDMpackets are transmitted over specific time intervals, the system caneasily separate the Doppler effect from other interferences. The use ofOFDM also allows for simple removal of noise from a signal, due to theuse of pre-determined sets of orthogonal frequencies.

Since OFDM supports MAC protocols with connectionless datagrambroadcast/multicast functionality, the system is able to provide abalanced network of nodes having the same function in the network. Thus,the present invention avoids segmentation of nodes within the networkand allows for removal of nodes without the network collapsing orbecoming inoperative. Also, in using a balanced network structureeliminates the need for continuous recalculation of the networkstructure, due to constant change in distance between nodes.

Through use of equal hierarchically ranked nodes, the system providesquick OFDM synchronization, which can be less than approximately 100milliseconds.

While the invention has been described in connection with one or moreembodiments, it is to be understood that the specific mechanisms andtechniques which have been described are merely illustrative of theprinciples of the invention, numerous modifications may be made to themethods and apparatus described without departing from the spirit andscope of the invention as defined by the appended claims

1. An object relative status determination system for a vehiclecomprising: at least one orthogonal frequency domain modulation (OFDM)transceiver generating a plurality of object range signals; and at leastone controller coupled to said at least one OFDM transceiver anddetermining object information relative to the vehicle in response tosaid plurality of object range signals.
 2. A system as in claim 1wherein said controller is coupled to a vehicle network.
 3. A system asin claim 2 wherein said vehicle network comprises: a head vehicle; atleast one middle vehicle; and a tail vehicle.
 4. An object relativestatus determination system for at least one vehicle comprising: atleast one OFDM transceiver generating at least one object range signal;at least one global navigation system (GNS) receiving at least onesatellite range signal; and at least one controller coupled to said atleast one OFDM transceiver and said at least one GPS and determiningobject information relative to a host vehicle in response to said atleast one satellite range signal and said at least one object rangesignal.
 5. A system as in claim 4 wherein said at least one OFDMtransceiver comprises: a first OFDM transceiver coupled within said hostvehicle and generating a first object range signal; and a second OFDMtransceiver coupled within the object and generating a second objectrange signal.
 6. A system as in claim 4 wherein said at least one GNScomprises: a first GPS coupled within said host vehicle and receiving afirst set of satellite range signals; and a second GPS coupled within anobject and receiving a second set of satellite range signals.
 7. Asystem as in claim 4 wherein said at least one controller determinesrelative range of at least one object with respect to said host vehiclein response to said at least one satellite range signal and said atleast one object range signal.
 8. A system as in claim 4 wherein said atleast one controller determines relative velocity of at least one objectwith respect to said host vehicle in response to said at least onesatellite range signal and said at least one object range signal.
 9. Asystem as in claim 4 wherein said at least one GNS comprises: at leastone GPS antenna; at least one radio frequency unit; and at least onedigital signal processor.
 10. A system as in claim 4 wherein said atleast one controller is coupled to a vehicle network.
 11. A system as inclaim 10 wherein said vehicle network comprises a platoon of vehicles.12. A system as in claim 4 wherein said at least one GNS receives aplurality of satellite range signals from a plurality of satellites. 13.A system as in claim 4 wherein said at least one GNS receives said atleast one satellite range signal from at least one GPS satellite.
 14. Asystem as in claim 4 wherein said at least one GNS receives said atleast one satellite range signal from at least one navy navigationsatellite system (NAVSAT) satellite.
 15. A system as in claim 4 whereinsaid at least one controller determines said object information relativeto said host vehicle in response to a single satellite range signal anda single object range signal.
 16. A system as in claim 4 wherein said atleast one controller determines said object information relative to saidhost vehicle in response to a plurality of object range signals.
 17. Asystem as in claim 4 wherein said at least one OFDM transceiverscomprise: a first OFDM transceiver coupled within said host vehicle; anda second OFDM transceiver coupled within an object and insynchronization with said first OFDM transceiver.
 18. A method ofdetermining object information relative to a vehicle comprising:receiving at least one satellite range signal; generating at least oneobject range signal utilizing at least one OFDM transceiver; anddetermining object information relative to the vehicle in response tosaid at least one satellite range signal and said at least one objectrange signal.
 19. A method as in claim 18 further comprising:determining range of a plurality of satellites relative to the vehicle;determining range of a plurality of satellites relative to an object;and determining range between the vehicle and the object utilizing saidat least one OFDM transceiver.
 20. A method as in claim 18 furthercomprising: determining range and rate of change in range between thevehicle and at least one satellite; and determining range and rate ofchange in range between the vehicle and at least one object via said atleast one OFDM transceiver.